tag:blogger.com,1999:blog-33841115235859325402017-12-12T19:59:40.549+01:00SeiðrSpace physics, Experiments, Inverse problems - Daily Reports (seiðr). Writings about various topics in plasma physics, radio science, space physics, rockets, radars, aurora, remote sensing, geophysics, radio astronomy, inverse problems, outdoors activities, electronics, and software defined radio. Juha Vierinennoreply@blogger.comBlogger123125tag:blogger.com,1999:blog-3384111523585932540.post-55723130249595703782017-12-12T19:58:00.002+01:002017-12-12T19:59:40.559+01:00Lunar mapping with 6-meter wavelength <div dir="ltr" style="text-align: left;" trbidi="on"><table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody><tr><td style="text-align: center;"><a href="https://1.bp.blogspot.com/-TR383mG74aA/WjAfTnWGH1I/AAAAAAAAQZ0/64XEo4KtYtwgBCRLT3fOudghpj37CMETwCLcBGAs/s1600/jro_moon.gif" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="600" data-original-width="800" height="300" src="https://1.bp.blogspot.com/-TR383mG74aA/WjAfTnWGH1I/AAAAAAAAQZ0/64XEo4KtYtwgBCRLT3fOudghpj37CMETwCLcBGAs/s400/jro_moon.gif" width="400" /></a></td></tr><tr><td class="tr-caption" style="text-align: center;">The animation sweeps from the southern hemisphere to the northern hemisphere. The equatorial region is poorly mapped, because one pixel of the range-Doppler image maps to a huge area on the Moon (this is apparent from the view above or below the Moon, which is nearly identical to the range-Doppler map of the Moon). The polar regions are mapped best.</td></tr></tbody></table><br />One of the efforts we are working on is mapping the Moon with 6-meter wavelength. This is done using the Jicamarca Radio Observatory 6-meter wavelength radar. The radar is useful for a number of reasons. The radar is huge. The dimensions of the antenna is 300 x 300 meters. It's got 9216 dipole antennas chained as groups of 12 colinear coaxial antennas. It can transmit up to 4 MW of power towards the Moon. It can be split into smaller sections for interferometry on receive. The antenna is fully polarimetric: you can transmit and receive any combination of two linear orthogonal polarizations. <br /><br />The most important reason for using Jicamarca is frequency. The low frequency of 49.92 MHz allows the radio wave to penetrate very deep into the subsurface of the Moon. We estimate that in highland regions, the wave can penetrate up to 1 km beneath the surface. The low frequency does come with an associated cost. It is not possible to make a very high resolution map of the Moon. We can only observe 10-15 minute passes, and the Moon only has a Doppler width of about 1 Hz at this frequency. The low frequency is also severely affected by ionospheric radio propagation, which modifies the polarization state of the wave, and contains phase noise due to small fluctuations in ionospheric electron density. <br /><br />This summer, we published our <a href="https://www.sciencedirect.com/science/article/pii/S0019103516308326">first paper</a> on the topic in the journal Icarus containing first results. Now we are planning to write a follow up study that goes more in depth. In order to compare our results with other observations of the Moon, we have been working towards projecting our range-Doppler map into lunar coordinates. This is now finally done, and we can now project our observations into any projection we want! The gif animation above shows the Moon projected into orthographic projection using Basemap and Matplotlib, which has a nifty warpimage function.<br /><div><br /></div><div>The key step towards projecting the measurements into arbitrary projections with Basemap is to make a cylindrically projected 2d image that has longitude (-180 to 180 degrees) on the x-axis and latitude (-90 to 90 degrees) on the y-axis. This image has to have a 2:1 ratio of pixels for the warpimage function to work correctly. This is what our image looks like:</div><table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody><tr><td style="text-align: center;"><a href="https://2.bp.blogspot.com/-8MJBGI0mp-E/WjAlKJVk7KI/AAAAAAAAQaI/yE7r6Ch2TuUhw0aqiEeInlNeF_09iZNngCLcBGAs/s1600/map2.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="800" data-original-width="1600" height="200" src="https://2.bp.blogspot.com/-8MJBGI0mp-E/WjAlKJVk7KI/AAAAAAAAQaI/yE7r6Ch2TuUhw0aqiEeInlNeF_09iZNngCLcBGAs/s400/map2.png" width="400" /></a></td></tr><tr><td class="tr-caption" style="text-align: center;">Depolarized radar return form the Moon in dB scale at 6-meter wavelength in cylindrical projection. Longitude (-180 to 180 degrees) in the x-axis and latitude (-90 to 90 degrees) on the y-axis. Obviously, no radar return is obtained from the far side of the Moon that is in the radar shadow. The Doppler equator region is poorly mapped, because a single range-Doppler bin maps into a very large geographic area. Also, interferometric separation of the north and south hemispheres also falls apart in the Doppler equator region.</td></tr></tbody></table><div><div>The animation shows the main characteristics of the map quite nicely. While the views from above and below look good, the equatorial region is very smeared and blobby. This is due to the fact that our measurement is fundamentally a range-Doppler map of the Moon. Regions near the equator map into a very large area on the Moon. Also, it is increasinly more difficult to separate the northern and southern hemisphere from one another using interferometry, because the angular separation near the Doppler equator is vanishingly small. Normally, one would simply not show the region near the equator, but we've opted to do this, to show that it is indeed crap.</div><div><br /></div><div>Here's some code, which shows how to use basemap to project an image in cylindrical coordinates into any projection supported by Basemap.</div><div><br /></div><div><code></code><br /><pre><code>fig = plt.figure()<br />fig.patch.set_facecolor('black')<br />b = Basemap(projection='ortho', lat_0 = lat_0, lon_0 = lon_0, <br /> resolution = 'l', area_thresh = 1000.)<br /># plot image with cylindrical projection onto basemap scene <br />b.warpimage(image=compf)<br /># draw the edge of the map <br />b.drawmapboundary(color="white")<br /># draw lat/lon grid lines every 30 degrees.<br />b.drawmeridians(np.arange(0, 360, 30),color="black")<br />b.drawparallels(np.arange(-90, 90, 30),color="black")<br /><br />plt.title("JRO 6-m depolarized return",color="white")<br />print(ofname)<br /># ensure that black color is used for the background<br />plt.savefig(ofname,facecolor=fig.get_facecolor())<br />plt.close()<br /></code></pre><code></code></div><div><br /></div><div><br /></div><div><br /></div></div></div>Juha Vierinenhttps://plus.google.com/108603317449900180332noreply@blogger.com0tag:blogger.com,1999:blog-3384111523585932540.post-27844461471000054282017-12-09T07:00:00.000+01:002017-12-09T07:00:06.704+01:00The Enchantress of Numbers<div class="separator" style="clear: both; text-align: center;"></div><div class="separator" style="clear: both; text-align: center;"></div><br /><br />&nbsp;For the anniversary of Ada Lovelace's birthday, let us celebrate the unlikely heroine who pioneered a field that, today, pervades nearly every aspect of our lives -- computer programming.<br /><br /><div class="separator" style="clear: both; text-align: center;"><a href="https://4.bp.blogspot.com/-o4nhxnvV-A8/WiZ_NUsZ-II/AAAAAAAAD30/la7kNkTK2MsVIsKnFS1xWPztMDrUhg5PwCLcBGAs/s1600/origin_001.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="700" data-original-width="560" src="https://4.bp.blogspot.com/-o4nhxnvV-A8/WiZ_NUsZ-II/AAAAAAAAD30/la7kNkTK2MsVIsKnFS1xWPztMDrUhg5PwCLcBGAs/s1600/origin_001.jpg" /></a></div><div style="text-align: center;"><span style="font-size: x-small;">From the brilliant and extraordinarily well-researched comic, <i><a href="http://sydneypadua.com/2dgoggles/" target="_blank">The Thrilling Adventures of Lovelace and Babbage</a> </i>by Sydney Padua.</span></div><br />Ada Lovelace was born in London in 1815, short months after news had reached England of the Duke of Wellington's victory over Napoleon at the battle of Waterloo.&nbsp; Romanticism was in full swing, and it was in the following year that <a href="http://www.radio-science.net/2017/11/scifi-through-ages-year-without-summer.html" target="_blank">Mary Shelley would conceive of the world's first work of science fiction, <i>Frankenstein</i></a>.<br /><br />Realism, the philosophical and artistic rebellion against the emotionality of Romanticism, was still several decades in the future, but Ada's mother had her own aspirations toward a rebellion against Romanticism: a hefty dose of math and science.<br /><br />At 17, Ada's mother hired Mary Somerville as a tutor, a respected researcher, science writer, and astronomer, who was later among the first female members of the Royal Astronomical Society along with Caroline Herschel.&nbsp; In 1833, Somerville also introduced Ada to her lasting friend and colleague, the engineer and inventor Charles Babbage.<br /><br />Shortly thereafter, dazzled by Ada's intellect, Babbage invited the young girl to work with his prototype for the Difference Engine, a series of numbered cogs and gears that functioned as a mechanical calculator.<br /><br /><br /><div class="separator" style="clear: both; text-align: center;"><a href="https://2.bp.blogspot.com/-Tg1omg-GhEI/WiaMuvTCdHI/AAAAAAAAD4U/toYnZ4VM6F0pc4E-KkGRYoVKmXTEUC0ygCLcBGAs/s1600/differenceengine.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="758" data-original-width="1200" height="404" src="https://2.bp.blogspot.com/-Tg1omg-GhEI/WiaMuvTCdHI/AAAAAAAAD4U/toYnZ4VM6F0pc4E-KkGRYoVKmXTEUC0ygCLcBGAs/s640/differenceengine.jpg" width="640" /></a></div><div style="text-align: center;"><span style="font-size: x-small;">The Difference Engine, a mechanical calculator designed to tabulate polynomial functions.</span></div><br />It was at seeing Ada's analytical capacity with the Difference Engine that Babbage called her "The Enchantress of Numbers."<br /><br />In the same year that Babbage met Ada Lovelace, he began to design a more generalized computational mechanism, which he called the Analytical Engine.&nbsp; A user could input programs and data via punched cards, and it would output printed numbers and curves.&nbsp; It could work with programmed loops, integrated memory, and conditional branching -- tasks familiar to any modern computer programmer-- and few scientists of the time could wrap their heads around the math required to understand the design.<br /><br /><div class="separator" style="clear: both; text-align: center;"><a href="https://2.bp.blogspot.com/-04tBS_Tw8Us/WiaBmq-RMQI/AAAAAAAAD4A/2OWKdtIP5OIF5Z-JY3ChrXzxxFgkFQ6aACLcBGAs/s1600/analyticalengine.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="676" data-original-width="1000" height="432" src="https://2.bp.blogspot.com/-04tBS_Tw8Us/WiaBmq-RMQI/AAAAAAAAD4A/2OWKdtIP5OIF5Z-JY3ChrXzxxFgkFQ6aACLcBGAs/s640/analyticalengine.jpg" width="640" /></a></div><div style="text-align: center;">&nbsp;<span style="font-size: x-small;">The Analytical Engine, by Sydney Padua.&nbsp; Available as a print <a href="https://www.redbubble.com/people/sydneypadua/works/15059232-babbages-analytical-engine" target="_blank">HERE</a>!</span></div><br /><br />Ada Lovelace wrote extensive notes in her translation of an article describing the Analytical Engine, including a detailed description of how to calculate Bernoulli numbers using the machine.&nbsp; Her method is widely considered to be the first-ever computer program.<br /><br /><div class="separator" style="clear: both; text-align: center;"><a href="https://upload.wikimedia.org/wikipedia/commons/thumb/c/cf/Diagram_for_the_computation_of_Bernoulli_numbers.jpg/800px-Diagram_for_the_computation_of_Bernoulli_numbers.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="560" data-original-width="800" height="448" src="https://upload.wikimedia.org/wikipedia/commons/thumb/c/cf/Diagram_for_the_computation_of_Bernoulli_numbers.jpg/800px-Diagram_for_the_computation_of_Bernoulli_numbers.jpg" width="640" /></a></div><div style="text-align: center;"><span style="font-size: x-small;"><a href="https://en.wikipedia.org/wiki/File:Diagram_for_the_computation_of_Bernoulli_numbers.jpg" target="_blank">Ada's "Diagram for the Computation of Bernoulli Numbers."</a></span></div><br /><br />&nbsp;In addition to her program, Ada described in her notes the ability of the Analytical Engine to solve problems of high complexity, including the possibility of writing programs to solve non-mathematical problems:<br /><br /><blockquote class="tr_bq">"[The Analytical Engine] might act upon other things besides <i>number</i>, were objects found whose mutual fundamental relations could be expressed by those of the abstract science of operations, and which should be also susceptible of adaptations to the action of the operating notation and mechanism of the engine...Supposing, for instance, that the fundamental relations of pitched sounds in the science of harmony and of musical composition were susceptible of such expression and adaptations, the engine might compose elaborate and scientific pieces of music of any degree of complexity or extent." </blockquote><blockquote class="tr_bq">(Ada's notes are all <a href="http://www.cs.yale.edu/homes/tap/Files/ada-lovelace-notes.html" target="_blank">here</a>)</blockquote><br />&nbsp;The transition from seeing the machine as a number-cruncher to a machine for manipulating symbols "is the fundamental transition from calculation to computation."*<br /><br /><br /><br />So while you spend your long, dark December hours programming, texting, or simply reading this blog via the Glorious Internet -- raise a glass(/teacup/mug) to the memory of Ada Lovelace, the Enchantress of Numbers, on her birthday.<br /><br /><div class="separator" style="clear: both; text-align: center;"><a href="https://upload.wikimedia.org/wikipedia/commons/thumb/a/a4/Ada_Lovelace_portrait.jpg/800px-Ada_Lovelace_portrait.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="800" data-original-width="557" height="640" src="https://upload.wikimedia.org/wikipedia/commons/thumb/a/a4/Ada_Lovelace_portrait.jpg/800px-Ada_Lovelace_portrait.jpg" width="443" /></a></div><div style="text-align: center;"><strike><span style="font-size: x-small;">and also her fabulous and mystifying hairdo</span></strike></div><div style="text-align: center;"></div><br />~~~~~~<br />* Taken from a quote by historian and Babbage specialist Doron Swade.Alessandra Serranohttp://www.blogger.com/profile/01802487750123767305noreply@blogger.com0tag:blogger.com,1999:blog-3384111523585932540.post-32321694378272162082017-12-07T06:00:00.000+01:002017-12-07T06:00:32.567+01:00Suomi 100 partyYesterday was the 100th anniversary of the Nation of Finland. And, to celebrate the event, we had a little party, with salmiakki, cake, more salmiakki, coffee, and even more salmiakki. We even improvised a small Finnish flag and played some finnish music. Here are some photos:<br /><br /><div class="separator" style="clear: both; text-align: center;"><a href="https://3.bp.blogspot.com/-80acB6lcvis/Wif5smjXWGI/AAAAAAAAEcM/xlgMCXp_-h4Cl9G7KF1p6CZQrp23egVJgCLcBGAs/s1600/Foto2008.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="1200" data-original-width="1600" height="240" src="https://3.bp.blogspot.com/-80acB6lcvis/Wif5smjXWGI/AAAAAAAAEcM/xlgMCXp_-h4Cl9G7KF1p6CZQrp23egVJgCLcBGAs/s320/Foto2008.jpg" width="320" /></a></div><br /><div class="separator" style="clear: both; text-align: center;"><a href="https://1.bp.blogspot.com/-xC-O3gVxYu4/Wif5uiI9rRI/AAAAAAAAEcQ/R9YyQOVq790y71EpqS6fMRPBjaydh6QgACLcBGAs/s1600/Foto2009.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="1600" data-original-width="1200" height="320" src="https://1.bp.blogspot.com/-xC-O3gVxYu4/Wif5uiI9rRI/AAAAAAAAEcQ/R9YyQOVq790y71EpqS6fMRPBjaydh6QgACLcBGAs/s320/Foto2009.jpg" width="240" /></a></div><br /><div style="text-align: center;"><i>Onnea Suomi!</i></div>Derek McKayhttp://www.blogger.com/profile/05310213628364646890noreply@blogger.com0tag:blogger.com,1999:blog-3384111523585932540.post-16890745708991196212017-12-06T06:12:00.000+01:002017-12-06T06:12:08.410+01:00Suomi 100<div class="separator" style="clear: both; text-align: center;"><a href="https://1.bp.blogspot.com/-UkkNXShFiyk/WiALqYoMIZI/AAAAAAAAEbc/LR0Z3wOrkCI6odJG-Q_2ReKjt9ix-N4GACLcBGAs/s1600/suomi_100.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="591" data-original-width="1170" height="161" src="https://1.bp.blogspot.com/-UkkNXShFiyk/WiALqYoMIZI/AAAAAAAAEbc/LR0Z3wOrkCI6odJG-Q_2ReKjt9ix-N4GACLcBGAs/s320/suomi_100.jpg" width="320" /></a></div><div style="text-align: center;"><br /></div><div style="text-align: center;">Today, 6th December 2017,&nbsp;</div><div style="text-align: center;">the nation of Finland celebrates&nbsp;</div><div style="text-align: center;">its 100th birthday.</div><div style="text-align: center;"><br /></div><div style="text-align: center;"><br /></div><div class="separator" style="clear: both; text-align: center;"><a href="https://4.bp.blogspot.com/-wftaqSIGmCg/WiANaZELZNI/AAAAAAAAEbw/ZysxgJNtbf4i1DywXiyex-dgF6ng4vqigCEwYBhgL/s1600/finland_flag.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="156" data-original-width="255" src="https://4.bp.blogspot.com/-wftaqSIGmCg/WiANaZELZNI/AAAAAAAAEbw/ZysxgJNtbf4i1DywXiyex-dgF6ng4vqigCEwYBhgL/s1600/finland_flag.png" /></a></div><div style="text-align: center;"><br /></div><div style="text-align: center;"></div><div style="text-align: center;"><br /></div><div style="text-align: center;"><br /></div><div style="text-align: center;"><i><span class="short_text" id="result_box" lang="fi"><span class="">Hyvää syntymäpäivää, Suomi.</span></span></i></div><div style="text-align: center;"><br /></div><div style="text-align: center;"><i><span class="short_text" id="result_box" lang="fi"><span class=""><span style="font-size: x-small;"><a href="http://suomifinland100.fi/">http://suomifinland100.fi/</a> </span></span></span></i></div><br />Derek McKayhttp://www.blogger.com/profile/05310213628364646890noreply@blogger.com0tag:blogger.com,1999:blog-3384111523585932540.post-11780429620888086192017-12-05T11:08:00.000+01:002017-12-05T11:08:47.653+01:00Saana illuminatedThe largest illumination art in the world was created at Kilpisjärvi to celebrate the 100th anniversary of Finland. Tomorrow, 6th December 2017, Finland celebrates the centenary of the founding of its nation. All across the country, there will be celebrations, festivities and a plethora of other events to celebrate 100 years of history.<br /><br />Part of the celebration includes the creation of artwork and, in the far northwest of the country the iconic mountain of Saana is being illuminated for the event.<br /><br />The entire mountain is being lit up in "Finnish blue". This is a massive scale, some 2,2 million square metres area. This makes it the largest illumination art work in the world.<br /><br /><br /><div class="separator" style="clear: both; text-align: center;"><a href="https://2.bp.blogspot.com/-NqnnEWm33NU/WiZrzuo9iaI/AAAAAAAAEb8/BpxdYcy0yq8HElNPl9kxgxvvT9Lsbr-fQCLcBGAs/s1600/saana_suomi100.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="768" data-original-width="1024" height="240" src="https://2.bp.blogspot.com/-NqnnEWm33NU/WiZrzuo9iaI/AAAAAAAAEb8/BpxdYcy0yq8HElNPl9kxgxvvT9Lsbr-fQCLcBGAs/s320/saana_suomi100.jpg" width="320" /></a></div><br /><br />The light art is created by a whole team of artists and technicians led by Kari Kola. The opening display was at 16:00 on Monday 04-Dec-2017, and the illumination will continue throughout the celebrations for the Suomi100 - Finland100. The display is part of a series of exhibitions, under the title of Luminous Finland 100.<br /><br />However, it is a challenging project, as December in Enontekiö is fraught with bad weather. As it turns out we had major snow storm in Tromsø last night and visibility is low. Saana is often wreathed in cloud. However, even if only briefly, the skies were clear enough to bath this epic Finnish landmark in light.<br /><br />But as it is kaamos (the time of year when the sun doesn't rise), then the display can run throughout. There is no sunrise or sunset, although there is the pale blue of the midday twilight.<br /><br /><br /><br /><a href="https://areena.yle.fi/1-4301969">https://areena.yle.fi/1-4301969</a>Derek McKayhttp://www.blogger.com/profile/05310213628364646890noreply@blogger.com0tag:blogger.com,1999:blog-3384111523585932540.post-59209283384306412022017-12-04T22:36:00.000+01:002017-12-04T22:36:43.801+01:00Adventures in USRP tuning<div class="separator" style="clear: both; text-align: center;"><a href="https://upload.wikimedia.org/wikipedia/commons/2/21/Radio_dial_from_Europe_from_1950.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="449" data-original-width="800" height="358" src="https://upload.wikimedia.org/wikipedia/commons/2/21/Radio_dial_from_Europe_from_1950.jpg" width="640" /></a></div><br />These days, USRP radios are prevalent in our corner of radio science. Where I'm writing from at MIT Haystack Observatory, we have many USRP flavors in use: N200, B210, B210 mini, and X310. Readers who are otherwise unfamiliar with USRPs may recognize the name from an earlier post on the <a href="http://www.radio-science.net/2017/08/eiscat-3d-demonstrator-array.html">EISCAT 3D demonstrator array</a>, which is using new custom N3x0 units. As a product line, I like USRPs because they are flexible, have the performance I want, and can be obtained at a reasonable price. Perhaps the most important feature, though, is that the USRPs run on and integrate well with open source software. At least, that's the key to this adventure.<br /><br />We recently acquired some <a href="https://www.ettus.com/product/details/X310-KIT">X310</a>s with <a href="https://www.ettus.com/product/details/UBX160">UBX daughterboards</a> to test them out as transmit units for geospace radar. Things were working reasonably well: set the center frequency of 440 MHz, feed the radio a waveform of our choosing, and the RF transmission would appear at the output as desired. Well, almost as desired. You see, the output at the tuning frequency is known to have a spurious tone, so <i>directly</i> tuning to the center frequency on transmit or receive is <a href="http://files.ettus.com/manual/page_general.html#general_tuning_process">not recommended</a>. In practice, the unwanted DC component is not so significant that it ruins the transmitted waveform. But being the perfectionist type, I wanted to see if I could eliminate it anyway. The typical solution is to tune to an offset frequency and do the final frequency shift digitally. The UHD software layer that runs the USRPs makes this easy; all one has to do is request a particular offset. However, requesting 440 MHz + 10 MHz offset (to keep the spurious signal well outside our waveform band) resulted in... an actual center frequency of 439999999.991 Hz and an offset of 10000000.009 Hz. Hmm. That gets rid of the DC spur, but now the tuning is subtly off. A 9 millihertz offset might work for most applications, but we want phase coherence over many pulses with a receiver that doesn't necessarily have the same small offset from 440 MHz. Time to investigate. Anyone not interested in the details of USRP tuning should move right along.<br /><br />After carefully reading the <a href="https://github.com/EttusResearch/uhd">UHD source code</a> (yay open source!) and experimenting with settings, I now think I know what is going on. Given a desired center frequency and local oscillator (LO) offset, the first thing the UHD software will do is calculate the desired RF frequency as (center_freq + lo_offset). It will then ask the daughterboard to try to tune that frequency, resulting in an actual RF frequency that may be slightly different. Then given the actual RF frequency and the desired center frequency, the software will calculate the desired digital signal processing (DSP) frequency as (actual_rf_freq - center_freq). Then it will ask the mainboard to set that digital frequency offset using the FPGA, resulting in an actual DSP frequency that may be slightly different.<br /><br />How this actually plays out depends on both on the USRP mainboard (X310, N200, B210, etc.) and on the tuner daughterboard in use (UBX, TwinRX, BasicRX, etc.). (Disclaimer: I'm going to make general statements here assuming that it works for all USRPs, but I haven't checked that and in actuality the details could be a little different. YMMV.) The common component for all of the radios is the DSP frequency correction on board the FPGA of the mainboard, so I'll start there. This is accomplished through a CORDIC stage on the FPGA, so the possible frequency steps end up being the mainboard clock rate divided by 2^32. So for the X3xx series with a clock rate of 200 MHz, this means possible DSP offsets must be a multiple of (200e6/2^32) = .046566 Hz. A DSP offset of 2 MHz, for instance, is not exactly possible (closest is 2.0000000018626451 MHz), but 1.5625 MHz, 3.125 MHz, 6.25 MHz, 12.5 MHz are (among many others). Of course, it is also necessary at a minimum to keep the DSP offset within half the bandwidth of the analog low-pass filter used by the daughterboard, so offsets can't be arbitrarily large.<br /><br />The other component is the RF tuning done by the daughterboard card, and for those there seems to be much more variety in architecture. Many will at some point involve a phase-locked loop (PLL) that tracks a desired frequency given a smaller reference, usually the daughterboard clock frequency divided by an integer divider. That reference frequency is then multiplied by either an integer factor (N) or a fractional factor of the form (N + K/4095), depending on the PLL mode used. UHD will let you adjust any of the following if the device supports it: the PLL mode between integer and fractional, the daughterboard clock frequency, and the integer divider that gives the PLL reference from the clock frequency. The latter is done by setting the tuning step size, which only applies in integer mode of the PLL. For specifics about what each daughterboard supports, the best resource I found is the <a href="https://github.com/EttusResearch/uhd/tree/maint/host/lib/usrp/dboard">source code itself</a>.<br /><br />So practically, there are 6 settings that I'm aware of that help you control USRP tuning:<br /><ol><li>Desired center frequency (center_freq)</li><li>Desired offset frequency (lo_offset)</li><li>Mainboard clock rate (master_clock_rate=X)</li><li>Daughterboard clock rate (dboard_clock_rate=X)</li><li>PLL mode (mode_n=[integer/fractional])</li><li>Integer-mode tuning step size (int_n_step=X)</li></ol>These can be set using the GNU Radio UHD module in Python as follows. <br /><pre style="background: #f1f1f1; color: black;"><span style="color: #2060a0;">from</span> gnuradio <span style="color: #2060a0;">import</span> uhd<br /></pre>The clock rates are set as part of the <a href="https://files.ettus.com/manual/page_configuration.html">device string</a>: <br /><pre style="background: #f1f1f1; color: black;">u <span style="color: #2060a0;">=</span> uhd.usrp_source(<br /> device_addr<span style="color: #2060a0;">=</span><span style="color: #c03030;">','</span>.join([<br /> <span style="color: #c03030;">"addr=192.168.10.2"</span>,<br /> <span style="color: #c03030;">"master_clock_rate=200e6"</span>,<br /> <span style="color: #c03030;">"dboard_clock_rate=20e6"</span>,<br /> ]),<br /> ...<br />)<br /></pre>The remaining settings are given as a <a href="https://files.ettus.com/manual/structuhd_1_1tune__request__t.html">tune_request object</a> and passed to the set_center_freq method: <br /><pre style="background: #f1f1f1; color: black;">req <span style="color: #2060a0;">=</span> uhd.tune_request(<br /> center_freq,<br /> lo_offset,<br /> args<span style="color: #2060a0;">=</span>uhd.device_addr(<span style="color: #c03030;">','</span>.join([<br /> <span style="color: #c03030;">"mode_n=integer"</span>,<br /> <span style="color: #c03030;">"int_n_step=100e3"</span>,<br /> ])),<br />)<br />u.set_center_freq(req, ch_num)<br /></pre><br />Returning to the inciting case, we now have a better way of setting a tuning offset while still resulting in a center frequency of exactly 440 MHz using the X310 and UBX daughterboard. First, set the daughterboard clock rate to 20 MHz, both because it is <a href="https://kb.ettus.com/UBX#Phase_Synchronization">recommended</a> and because it allows us to control the input frequency into the PLL. Then, set the PLL mode to "integer" and give a tuning step size of 100 kHz, which is possible because (20e6/100e3) = 200 gives a small integer divider for getting the PLL reference frequency from the daughterboard clock frequency. Now we know we can exactly tune any RF frequency that is a multiple of 100 kHz. Finally, knowing that the master clock rate is 200 MHz so that possible DSP offsets must be a multiple of (200e6/2^32), choose a desired LO offset of 12.5 MHz (=200e6/16). This gives a desired RF frequency of 452.5 MHz, which is a multiple of 100 kHz. This results in a 440 MHz tuning that is exact. Incidentally, we now know that the original direct exact tuning of 440 MHz was a bit of a fluke: it just so happens that 440 MHz is an exact fractional multiple of the default UBX clock rate of 50 MHz, i.e. (8&nbsp;+ 3276/4095)*50e6 = 440e6.<br /><br />If you've made it this far, hopefully you will find this information useful! Now go forth and tune some USRPs.Ryan Volzhttps://plus.google.com/100034201842656194567noreply@blogger.com1tag:blogger.com,1999:blog-3384111523585932540.post-21034625051828950452017-11-24T07:30:00.000+01:002017-11-24T13:06:07.867+01:00'Oumuamua<div class="separator" style="clear: both; text-align: center;"><a href="https://www.jpl.nasa.gov/images/comet/20171026/comet20171025-16.gif" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="450" data-original-width="800" height="360" src="https://www.jpl.nasa.gov/images/comet/20171026/comet20171025-16.gif" width="640" /></a></div><br />In the Hawaiian language, the name <i>'Oumuamua</i> roughly translates to "scout" or "messenger" from a distant path.&nbsp; It is an apt name for the first detected interstellar object within our solar system.<br /><br />The discovery was published November 20th, 2017 in <a href="https://www.nature.com/articles/nature25020.pdf" target="_blank">Nature</a>, with further observations presented in <a href="http://www2.ess.ucla.edu/~jewitt/papers/2017/JLR17.pdf" target="_blank">this paper</a>, in part by UiT's own Jane Luu! <br /><br /><br /><div class="separator" style="clear: both; text-align: center;"><a href="https://4.bp.blogspot.com/-VwSPHT2IQRk/WhbPIa-6HgI/AAAAAAAAD3Q/41ig3h6Y_3UFfgGMLaIa38gakqlhKhyCACLcBGAs/s1600/Screen%2BShot%2B2017-11-23%2Bat%2B14.32.46.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="592" data-original-width="1178" height="320" src="https://4.bp.blogspot.com/-VwSPHT2IQRk/WhbPIa-6HgI/AAAAAAAAD3Q/41ig3h6Y_3UFfgGMLaIa38gakqlhKhyCACLcBGAs/s640/Screen%2BShot%2B2017-11-23%2Bat%2B14.32.46.png" width="640" /></a></div><div style="text-align: center;">Figure from Nature (<a href="https://www.nature.com/articles/nature25020.pdf" target="_blank">source</a>).&nbsp; (a) shows the presence of object 'Oumuamua, appearing as a streak of motion in relation to background stars.&nbsp; In (b), observations were made tracking at the objects rate, and show no signs of a coma or "tail", indicating that the object is most likely rocky or metallic (like an asteroid) as opposed to cometlike.</div><br />Initial observation showed an object zipping rapidly relative to background stellar motion, traveling around 95,000 km/hr.&nbsp; An international team of astronomers, led by Karen Meech, had to act fast: by the time 'Oumuamua was detected, it had already swung around its closest approach to the Sun and was on its way back out of our solar system.&nbsp; Data from observations between October 14-30 were able to refine the model of orbital trajectory to a precision &gt;100σ.&nbsp; Unlike all other known asteroids and comets, this object could not possibly have originated from within our solar system, nor even from the comet-kingdom surrounding us known as the Kuiper belt.&nbsp; Instead, 'Oumuamua was from far, far beyond in interstellar space.<br /><br />Lightcurve and spectral analysis was able to tell us more about 'Oumuamua.&nbsp; From the mean magnitude, a mean radius of around 100m was able to be deduced.&nbsp; However, there was a very large 2.5-magnitude lightcurve range, indicating that 'Oumuamua is either two-toned (which spectral analysis disproved, concluding the object has uniform color over the entire surface) or very elongated, with rotational motion giving rise to the object reflecting in this irregular manner.&nbsp; The rotational period is around 7 hours, not uncommon for an object of this size, and has an elongated axis ratio around 10:1.<br /><br />So we have, as the astronomers put it, a "cigar" shaped asteroid, spinning rapidly and originating from beyond our solar system.&nbsp; It could be possible to pinpoint the general region of origin, but further work is needed for this.<br /><br /><div class="separator" style="clear: both; text-align: center;"><a href="http://en.es-static.us/upl/2017/11/interstellar-asteroid-Oumuamua-artist-e1511206368400.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" src="http://en.es-static.us/upl/2017/11/interstellar-asteroid-Oumuamua-artist-e1511206368400.jpg" data-original-height="541" data-original-width="800" height="432" width="640" /></a></div><div style="text-align: center;"><strike>(It's definitely NOT an alien spaceship)</strike></div><br /><br /><br /><br /><br /><br />Alessandra Serranohttp://www.blogger.com/profile/01802487750123767305noreply@blogger.com0tag:blogger.com,1999:blog-3384111523585932540.post-49502296315099329582017-11-22T12:55:00.002+01:002017-11-22T13:12:53.834+01:00Severe weather warning<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody><tr><td style="text-align: center;"><a href="https://1.bp.blogspot.com/-UKuyMJpTsJk/WhVmrnya3HI/AAAAAAAAEbA/vRp_ecIIRG0uaLHQjSJWd55hvTAM8UUMgCLcBGAs/s1600/kaira_blizzard.jpg" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="226" data-original-width="956" height="148" src="https://1.bp.blogspot.com/-UKuyMJpTsJk/WhVmrnya3HI/AAAAAAAAEbA/vRp_ecIIRG0uaLHQjSJWd55hvTAM8UUMgCLcBGAs/s640/kaira_blizzard.jpg" width="640" /></a></td></tr><tr><td class="tr-caption" style="text-align: center;"><span style="font-size: xx-small;">High winds at the KAIRA site at Kilpisjärvi. Photo: D. McKay.</span></td></tr></tbody></table><br /><br />Extreme weather is expected tomorrow in the Troms area. Here is the warning from the Norwegian Weather Information server (yr.no).<br /><br /><br /><blockquote class="tr_bq"><b>Ekstremvarsel</b><br /><br /><b>Navn</b> Ylva <br /><b>Område</b> Helgeland, Saltfjellet, Salten og Ofoten Troms <br /><b>Fase</b> B <br /><b>Tidspunkt</b> onsdag 22. november kl 11:30 <br /><br /><b>Meldingen om ekstremværet «Ylva» gjelder for Helgeland, Saltfjellet, Salten og Ofoten </b><br /><br />Onsdag kveld ventes økning til søraustlig full storm utsatte steder med lokalt kraftige vindkast på 40-50 m/s. Vinden er ventet å minke torsdag kveld i sør, i nord først fredag morgen.<br /><br /><b>Troms </b><br /><br />Torsdag morgen ventes økning til søraustlig full storm utsatte steder med lokalt kraftige vindkast på 35-45 m/s. Vinden er ventet å minke fredag morgen.</blockquote><blockquote class="tr_bq"><b>Beskrivelse av værsituasjonen: </b><br /><br />Lavtrykk i Norskehavet og høytrykk over Kola-halvøya setter opp et kraftig sørøstlig vindfelt over deler av Nord-Norge. Med denne vindretningen ventes store lokale variasjoner i vindstyrke, og det kan forventes kraftige vindkast på 35-50 m/s i utsatte fjordstrøk og andre leområder. <br /><br />Det blir stor fare for innstillinger av flyavganger, båter og annen transport. Broer og fjelloverganger kan bli stengt. Det kan være farlig å oppholde seg utendørs. Det ventes uvanlig stor skade på bygninger, infrastruktur, strømnett og skog. </blockquote>Ref: <a href="https://www.yr.no/spesialvarsel/ekstrem.html">https://www.yr.no/spesialvarsel/ekstrem.html</a> <br /><br /><br /><br /><table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody><tr><td style="text-align: center;"><a href="https://1.bp.blogspot.com/-gM1DEF5amOA/WhVphgXV7FI/AAAAAAAAEbM/11haBqqY0RQ0M10qN-AcIOOH17VyUTGZACLcBGAs/s1600/meteogram_troms_20171122.jpg" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="307" data-original-width="921" height="212" src="https://1.bp.blogspot.com/-gM1DEF5amOA/WhVphgXV7FI/AAAAAAAAEbM/11haBqqY0RQ0M10qN-AcIOOH17VyUTGZACLcBGAs/s640/meteogram_troms_20171122.jpg" width="640" /></a></td></tr><tr><td class="tr-caption" style="text-align: center;">Weather forecast from yr.no, as of 12:00 UTC on 22-Nov-2017.</td></tr></tbody></table>Derek McKayhttp://www.blogger.com/profile/05310213628364646890noreply@blogger.com0tag:blogger.com,1999:blog-3384111523585932540.post-20703420694358086222017-11-21T07:00:00.000+01:002017-11-21T11:22:47.698+01:00SciFi Through the Ages: The Year Without a Summer<div class="separator" style="clear: both; text-align: center;"><a href="https://4.bp.blogspot.com/-7Fv9TAAJ8q0/WhLLfdyZncI/AAAAAAAAD3A/-2_l2ujriuQ-njb5_FVCu_E69MYh2SXRQCLcBGAs/s1600/452551e0289dc04a90958c9d79ac9e91.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="600" data-original-width="439" height="400" src="https://4.bp.blogspot.com/-7Fv9TAAJ8q0/WhLLfdyZncI/AAAAAAAAD3A/-2_l2ujriuQ-njb5_FVCu_E69MYh2SXRQCLcBGAs/s400/452551e0289dc04a90958c9d79ac9e91.jpg" width="292" /></a></div><br />At the close of the 18th century, two Italian scientists were electrocuting frogs.<br /><br />Luigi Galvani and Alessandro Volta were pioneering the subject of galvanism, studying the effects of electricity on muscle contractions in biological matter.&nbsp; By touching the legs of a dead frog with a pair of electrodes, they were able to see the legs twitch upward, as though reimbued with life.<br /><br />1803 was the year that galvanism left the laboratory and entered the public consciousness, when Galvani's nephew, Giovanni Aldini, held a public demonstration in Newgate Prison in London.&nbsp; By running an electric current through the corpse of an executed criminal, the deceased limbs were seen to be "<a href="https://en.wikipedia.org/wiki/Galvanism#cite_note-7" target="_blank">set in motion</a>", the dead man's hand raising and clenching into a fist, his jaw quivering and contorting, and his eye opening to the attending audience.<br /><br />1815 was a year that saw one of Earth's most massive and violent volcanic eruptions.&nbsp; Mount Tambora, on one of the islands of Indonesia, ejected around 160 cubic kilometers(!!) of tephra into the air, temporarily cloaking the planet in a dark, volcanic shroud, deflecting sunlight and darkening skies across the globe.<br /><br />1816, the year that followed, would come to be known as "The Year Without a Summer": average temperatures dropped, and severe frosts led to agricultural failure and extreme food shortages. <br /><br />Galvani's frog, Aldini's reanimated criminal, and a world darkened by volcanic ash combined to create the setting.&nbsp; It was during the purely nominal summer of that year that a teenaged girl lay awake in a darkened villa on Lake Geneva, possessed by ghost stories.<br /><br /><br /><blockquote class="tr_bq">"I saw the pale student of unhallowed arts kneeling beside the thing he had put together. I saw the hideous phantasm of a man stretched out, and then, on the working of some powerful engine, show signs of life, and stir with an uneasy, half vital motion. Frightful must it be; for supremely frightful would be the effect of any human endeavour to mock the stupendous mechanism of the Creator of the world."** (<a href="https://en.wikipedia.org/wiki/Frankenstein#cite_note-16" target="_blank">Mary Shelley</a>) </blockquote><br /><br />And so Mary Shelley, at 18 years old, brought <i>Frankenstein</i> into the world.<br /><br />Though her work was originally classified as gothic horror, its direct inspiration from contemporary scientific research has led to it being widely credited as the first true example of a new kind of literature: Science Fiction.<br /><br />Though future posts will consider earlier works that I consider "proto-science fiction", <i>Frankenstein</i> achieved something no work had before it: the use of story as a laboratory for creatively experimenting with newfound scientific research.&nbsp; Science fiction invites us to look at our new understanding and ask: "What is possible? And what are the implications?"<br /><br /><br />Going forward, and in no particular order, I thought it would be a fun addition to this blog to have some posts on science fiction, its connections to the science that inspired it, and the merits of philosophical investigation into scientific topics.&nbsp; Other blog writers are encouraged to contribute their own musings on their own favorite works or authors as well!<br /><br /><br /><br />~~~~~~~~~~~~~~<br /><br />** The author of this post feels a tug of familiarity at this description of "the pale student of unhallowed arts kneeling beside the thing [s]he had put together."&nbsp; Frightful it is, indeed.Alessandra Serranohttp://www.blogger.com/profile/01802487750123767305noreply@blogger.com0tag:blogger.com,1999:blog-3384111523585932540.post-62880329439542128722017-11-17T09:08:00.000+01:002017-11-17T09:56:30.111+01:00Meteor over Finland 2017-11-16<br />Following on from the previous post, by co-incidence there was a major fireball over Finland. This has been seen also from parts of Norway.<br /><br /><div><br /></div><div class="separator" style="clear: both; text-align: center;"><a href="https://1.bp.blogspot.com/-Kc3pZ6y02qI/Wg6YsGtVlNI/AAAAAAAAEaw/EvsX0jI7Qkw6vq0Kvzx_o9AXsWehAJIzgCLcBGAs/s1600/meteor_finland_20171116.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="511" data-original-width="794" height="205" src="https://1.bp.blogspot.com/-Kc3pZ6y02qI/Wg6YsGtVlNI/AAAAAAAAEaw/EvsX0jI7Qkw6vq0Kvzx_o9AXsWehAJIzgCLcBGAs/s320/meteor_finland_20171116.jpg" width="320" /></a></div><div><br /></div><div>Here are some links (mostly in Finnish).</div><div></div><ul><li><a href="https://yle.fi/uutiset/3-9935407">https://yle.fi/uutiset/3-9935407</a></li><li><a href="https://yle.fi/uutiset/3-9935296">https://yle.fi/uutiset/3-9935296</a></li><li><a href="https://www.taivaanvahti.fi/observations/show/68340">https://www.taivaanvahti.fi/observations/show/68340</a></li></ul><br /><br />Curiously, the last time we did some asteroid observations there was a co-incident <a href="http://kaira.sgo.fi/2013/02/are-2012-da14-and-chelyabinsk-meteor.html">meteor over Chelyabinsk</a>.Derek McKayhttp://www.blogger.com/profile/05310213628364646890noreply@blogger.com0tag:blogger.com,1999:blog-3384111523585932540.post-50001513878899271952017-11-13T08:14:00.000+01:002017-11-17T08:59:13.100+01:00Meteor Showers<div class="separator" style="clear: both; text-align: center;"><a href="https://1.bp.blogspot.com/-1fdLltILRpI/WfyFNT9odUI/AAAAAAAAD2Y/vufqLKtCUa4zwvNIIvJBv0J-KhFd9dIOwCLcBGAs/s1600/Pix-1833Meteors-AdventistDrawing-600x750.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="750" data-original-width="600" height="640" src="https://1.bp.blogspot.com/-1fdLltILRpI/WfyFNT9odUI/AAAAAAAAD2Y/vufqLKtCUa4zwvNIIvJBv0J-KhFd9dIOwCLcBGAs/s640/Pix-1833Meteors-AdventistDrawing-600x750.jpg" width="512" /></a></div>On the night of November 13, 1833, the astronomer Denison Olmsted was awoken by his neighbors and ran outside to a sky alight with over 72,000 meteors an hour -- roughly 20 a second.&nbsp; This spectacular meteor shower became the subject of several woodcuts, and I find them delightful, so I will put them here.<br /><br /><div class="separator" style="clear: both; text-align: center;"><a href="https://4.bp.blogspot.com/-EZIxiIXY0x4/WfyFNWXLmMI/AAAAAAAAD2Q/9Skhve3vV_gBYP-E0Mj2UleyHV95oLoSwCLcBGAs/s1600/1-leonid-meteor-shower-1833-granger.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="524" data-original-width="900" height="372" src="https://4.bp.blogspot.com/-EZIxiIXY0x4/WfyFNWXLmMI/AAAAAAAAD2Q/9Skhve3vV_gBYP-E0Mj2UleyHV95oLoSwCLcBGAs/s640/1-leonid-meteor-shower-1833-granger.jpg" width="640" /></a></div><br /><br /><br /><div class="separator" style="clear: both; text-align: center;"><a href="https://2.bp.blogspot.com/-hrWSuJnVNpI/WfyFNYzU7eI/AAAAAAAAD2U/3L-dabvTzcgB707PcPAoXA7Q1xxY-51ZgCLcBGAs/s1600/6637d5738a061580a03a04fdee28d633.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="900" data-original-width="589" height="640" src="https://2.bp.blogspot.com/-hrWSuJnVNpI/WfyFNYzU7eI/AAAAAAAAD2U/3L-dabvTzcgB707PcPAoXA7Q1xxY-51ZgCLcBGAs/s640/6637d5738a061580a03a04fdee28d633.jpg" width="418" /></a></div><br /><div class="separator" style="clear: both; text-align: center;"><a href="https://4.bp.blogspot.com/-HgpIcpVaK6Q/WfyFOHPuF4I/AAAAAAAAD2c/IBXKgWyhWRkBA9IxTMWffc1Ofgeqg23igCLcBGAs/s1600/ce085ec63ccfe6b8a03d655d492f5bba.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="720" data-original-width="489" height="640" src="https://4.bp.blogspot.com/-HgpIcpVaK6Q/WfyFOHPuF4I/AAAAAAAAD2c/IBXKgWyhWRkBA9IxTMWffc1Ofgeqg23igCLcBGAs/s640/ce085ec63ccfe6b8a03d655d492f5bba.jpg" width="434" /></a></div><br />Meteor shower season is almost upon us!&nbsp; Each shower is named for the constellation radiant point (i.e., Leonids radiate from the constellation Leo, etc.) <br /><br /><b>Leonid shower peaks around November 17</b><br /><b>Northern Taurids visible through December 10</b><br /><b>Southern Taurids visible through November 30, and</b><br /><b>Orionids peaks during the night of November 28</b><br /><br />Unfortunately, none of these meteor showers are quite expected to reach the extreme that Olmsted saw in 1833 -- but it's always a good excuse to go watch the night sky.<b> </b>Alessandra Serranohttp://www.blogger.com/profile/01802487750123767305noreply@blogger.com0tag:blogger.com,1999:blog-3384111523585932540.post-87450190244076350192017-11-10T08:00:00.000+01:002017-11-10T08:00:13.064+01:00Lego aeroplanesTomorrow is the Turneringsdag 2017 for First Lego League, with an event scheduled in Tromsø. Details: <a href="http://hjernekraft.org/turnering/473/tromso/forsiden.aspx">http://hjernekraft.org/turnering/473/tromso/forsiden.aspx</a><br /><br />However, this reminded me of the last time I flew into Tromsø. I had been on a flight from Oslo to Tromsø and, on landing, I was immediately whisked off to a Lego-building project.<br /><br />Standard.<br /><br />The assignment for that evening was the construction of an airliner. Here is what the team put together. Not a half-bad effort if you ask me...<br /><br /><br /><div class="separator" style="clear: both; text-align: center;"><a href="https://4.bp.blogspot.com/-1GB3JGz4lK0/WgMFTRrBF0I/AAAAAAAAEac/VwZtab1O23M0Em_P-JGlXi5V7sagDm0rgCLcBGAs/s1600/Foto1679.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="1200" data-original-width="1600" height="240" src="https://4.bp.blogspot.com/-1GB3JGz4lK0/WgMFTRrBF0I/AAAAAAAAEac/VwZtab1O23M0Em_P-JGlXi5V7sagDm0rgCLcBGAs/s320/Foto1679.jpg" width="320" /></a></div><br />But some time later, I was going through my photographs and found a rather odd coincidence. Yes, I had taken that photograph of&nbsp; the Lego aircraft. But the photo immediately prior to it was one taken out of the window of the aeroplane on my flight into Tromsø.<br /><br />What I find rather disturbing is the condition of the wing, with streams of dirt and soot and missing paint. Seriously, click on the photo and take a look yourself! That aircraft has definitely seen better days. I do hope the ground crew take a careful look at it.<br /><br /><br /><div class="separator" style="clear: both; text-align: center;"><a href="https://1.bp.blogspot.com/-BQCa4_h6bZM/WgMFTu34F0I/AAAAAAAAEag/R5583eOECvgS3B2opZosMXkhroAXfMVJgCLcBGAs/s1600/Foto1678.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="1600" data-original-width="1200" height="320" src="https://1.bp.blogspot.com/-BQCa4_h6bZM/WgMFTu34F0I/AAAAAAAAEag/R5583eOECvgS3B2opZosMXkhroAXfMVJgCLcBGAs/s320/Foto1678.jpg" width="240" /></a></div><br /><br />But the juxtaposition between the adjacent photos of the real aeroplane and the Lego model in the photo set was quite amusing.<br /><br />And, yeah... the Lego one is way cooler.Derek McKayhttp://www.blogger.com/profile/05310213628364646890noreply@blogger.com0tag:blogger.com,1999:blog-3384111523585932540.post-13522151206611404322017-11-09T06:30:00.000+01:002017-11-09T06:30:03.648+01:00Happy Birthday, Carl Sagan!<div class="separator" style="clear: both; text-align: center;"><a href="https://2.bp.blogspot.com/-Rndx4Jt-wIs/WfxLEYtOmnI/AAAAAAAAD2A/X1zxfhHKzMUzyMr5mcl5QZDUb6zzvFm1gCLcBGAs/s1600/carl-sagan-quotes-640x480.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="480" data-original-width="640" height="480" src="https://2.bp.blogspot.com/-Rndx4Jt-wIs/WfxLEYtOmnI/AAAAAAAAD2A/X1zxfhHKzMUzyMr5mcl5QZDUb6zzvFm1gCLcBGAs/s640/carl-sagan-quotes-640x480.jpg" width="640" /></a></div><blockquote class="tr_bq">“At the heart of science is an essential balance between two seemingly contradictory attitudes — an openness to new ideas, no matter how bizarre or counterintuitive they may be, and the most ruthless skeptical scrutiny of all ideas, old and new.&nbsp; This is how deep truths are winnowed from deep nonsense.”</blockquote>Whenever I'm feeling down about science, about my ability to be a scientist, about the futility of trying to wring any meaning whatsoever from the universe, I just think of the wise words of Carl Sagan.&nbsp; He was probably the first to articulate the conflict between my love for science and my loathing of science <i>classes</i>.&nbsp; “Every kid starts out as a natural-born scientist," he says, "and then we beat it out of them.&nbsp; Few trickle through the system with their wonder and enthusiasm for science intact.”<br /><br />He is ever an inspiration for being an effective and passionate science communicator.<br /><br />So, happy birthday, Carl Sagan!&nbsp; Your star-stuff lives on. Alessandra Serranohttp://www.blogger.com/profile/01802487750123767305noreply@blogger.com0tag:blogger.com,1999:blog-3384111523585932540.post-19516629655855178692017-11-08T08:00:00.000+01:002017-11-08T14:10:16.386+01:00KAIRA backupsThere are several backups of selected sections of the KAIRA data set held at UiT. One is a small data farm which is located in the PhD office. Each disk is a few terabytes. But there is a rather odd arrangement for supporting them.<br /><br /><div class="separator" style="clear: both; text-align: center;"><a href="https://4.bp.blogspot.com/-98qMJUEdDHs/WgMAUFsFf3I/AAAAAAAAEaM/dN5_0fC-itMeBg7APgqrf7LANpVRqzUfwCLcBGAs/s1600/Foto1201.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="600" data-original-width="800" height="240" src="https://4.bp.blogspot.com/-98qMJUEdDHs/WgMAUFsFf3I/AAAAAAAAEaM/dN5_0fC-itMeBg7APgqrf7LANpVRqzUfwCLcBGAs/s320/Foto1201.jpg" width="320" /></a></div><br />All the cardboard and paper and plastic around the black disk boxes serves a purpose. The cardboard underneath is sound insulation, to keep the noise down in what is otherwise a quiet work room. The cardboard on the sides and the collar at the top is to hold the disks in place. You certainly don't want one accidentally knocked over! These also keep the disks spaced apart from each other for thermal reasons. The covers at the top are partly thermal but mostly to stop dust settling on the disks when they are powered down.<br /><br />The cabling to the side is the USB3.0 distribution network, along with a power bus. Oh, and there is emergency tea... just in case!<br /><br />There is some speculation that the cover of the top is a reference to the arches of <a href="http://www.radio-science.net/2017/09/at-mountains-of-madness.html">antediluvian temples</a> that&nbsp; dot the Tromsø landscape. But that is just paranoia. Or is it...?Derek McKayhttp://www.blogger.com/profile/05310213628364646890noreply@blogger.com1tag:blogger.com,1999:blog-3384111523585932540.post-27900674998099955632017-11-05T21:59:00.002+01:002017-11-06T11:37:51.853+01:00LIGO signal processing in two lines of code<div dir="ltr" style="text-align: left;" trbidi="on"><table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody><tr><td style="text-align: center;"><a href="https://1.bp.blogspot.com/-LGl4ACexXMU/Wf96jXqQW5I/AAAAAAAAP14/GCGVihrHnlsNfJgPIWk-ZrH-23TypO7eACLcBGAs/s1600/simple.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="600" data-original-width="800" height="240" src="https://1.bp.blogspot.com/-LGl4ACexXMU/Wf96jXqQW5I/AAAAAAAAP14/GCGVihrHnlsNfJgPIWk-ZrH-23TypO7eACLcBGAs/s320/simple.png" width="320" /></a></td></tr><tr><td class="tr-caption" style="font-size: 12.8px;">Two lines of signal processing will dig out the gravitational wave signal!</td></tr></tbody></table>This year’s Nobel prize in physics was awarded to Rainer Weiss, Barry C. Barish, and Kip Thorn<br />for the discovery of gravitational waves. Only two years earlier, on September 14 2015, 09:50:45<br />UTC, the two Laser Interferometer Gravitational-Wave Observatory (LIGO) instruments detected<br />a gravitational wave for the first time in history. This event was perhaps the most important<br />scientific discovery since the detection of the Higg’s boson by CERN. The existence of gravitational<br />waves had been predicted by Einstein’s general theory relativity, but never before detected.<br /><br />The gravitational wave event detected by LIGO is thought to be from a collision of two black<br />holes, which sends out a localized chirp like pulse in the space-time. LIGO utilizes two detectors,<br />which are spaced approximately 3000 km apart. These detectors measure strain (∆L/L) as a function of time. Here ∆L is the variation in length and L is the total length in which the variation is measured.<br />In other words, strain is the normalized variation in length L of the interferometer line due to<br />gravitational-wave induced ripples in space-time.<br /><br />LIGO uses two geographically separated stations to measure gravitional waves: Hanford, WA<br />(H1), and Livingston, LA (L1). The gravitational wave propagates at the speed of light c ≈ 3e8<br />m/s. If the same signal is detected at two different places with a time difference less than or equal<br />to the speed of light propagation time between the sensors, then this provides assurance that the<br />event is in fact real, and not caused by e.g., local seismic activity. Now with three stations, triangulation can be used to determine direction of arrival for LIGO events!<br /><br />The LIGO data is severely corrupted with instrumental noise. This noise is much larger in<br />amplitude than the gravitational wave signal. However, this noise is very narrow band in nature,<br />and it can be filtered out using relatively basic signal processing techniques. Such filtering is<br />routinely used by LIGO to improve the sensitivity of the instrument.<br /><br />In fact the signal processing techniques are so simple that an undergraduate can implement them from scratch in a few weeks. That is exactly what I had my students do for their midterm exam in the signal processing course this year. Out of 46 students 45 managed to dig out the gravitational wave signal on their own, albeit with some specific instructions on what sort of techniques to use.<br /><br />I didn't want the students to just copy the <a href="https://losc.ligo.org/s/events/GW150914/GW150914_tutorial.html">publicly available LIGO signal processing tutorial,</a> so I though I'd send the students down a slightly different path, which is even more simple than the one in the tutorial. My course is a very basic one, which doesn't cover statistical aspects of signals, so this technique involves no statistical processing!<br /><br />In fact, it is possible to boil down LIGO signal processing into just two lines of code. Here's what I came up with:<br /><code></code><pre><code># Dig out the LIGO signal<br /># whiten spectrum and lowpass<br />def whiten_and_lp(z,L=8):<br /> Z=rfft(s.tukey(z.size)*z,z.size)<br /> return(irfft(rfft(n.repeat(1.0/L,L),z.size)*Z/n.abs(Z)).real)<br /></code></pre><code></code><br />Technically, I guess I could have reduced this to one line, but that wouldn't have fit the line width on this blog post.<br /><br />The full code, which includes reading LIGO files and plotting is shown below. You can download the data&nbsp;<a href="https://losc.ligo.org/s/events/GW150914/H-H1_LOSC_4_V2-1126259446-32.hdf5">here</a>&nbsp;and&nbsp;<a href="https://losc.ligo.org/s/events/GW150914/H-H1_LOSC_4_V2-1126259446-32.hdf5">here.</a><br /><br /><code></code><br /><pre><code>#!/usr/bin/env python<br />#<br /># Signal processing to clean up mechanical vibrations from LIGO data.<br /># The idea is to use very simple signal processing concepts. <br />#<br /># (c) 2017 Juha Vierinen<br />#<br />import numpy as n<br />from numpy.fft import rfft<br />from numpy.fft import irfft<br />import h5py as h<br />import scipy.signal as s<br />import matplotlib.pyplot as plt<br /><br /># Dig out the LIGO signal<br /># whiten spectrum and lowpass<br />def whiten_and_lp(z,L=8):<br /> Z=rfft(s.tukey(z.size)*z,z.size)<br /> return(irfft(rfft(n.repeat(1.0/L,L),z.size)*Z/n.abs(Z)).real)<br /><br /># Read strain data<br />sh1=h.File("H-H1_LOSC_4_V2-1126259446-32.hdf5","r")["strain/Strain"].value<br />sl1=h.File("L-L1_LOSC_4_V2-1126259446-32.hdf5","r")["strain/Strain"].value<br /><br /># sample rate (Hz)<br />fs=4096.0<br /><br /># time vector (seconds)<br />t=n.arange(len(sh1))/fs<br /><br /># Whiten and lowpass filter Livingston and Hanford signals<br />wsh1=whiten_and_lp(sh1)<br />wsl1=whiten_and_lp(sl1)<br /><br /># Plot whitened and low-pass filtered signal<br />plt.plot(t,wsh1,label="Hanford") <br />plt.plot(t,wsl1,label="Livingston") <br />plt.xlabel("Time (s)")<br />plt.ylabel("Whitened strain")<br />plt.title("Whitened and low-pass filtered signal")<br />plt.legend()<br />plt.xlim([16.2,16.5])<br />plt.show()<br /></code></pre><code></code><br /><pre></pre></div>Juha Vierinenhttps://plus.google.com/108603317449900180332noreply@blogger.com0tag:blogger.com,1999:blog-3384111523585932540.post-28221345115399666162017-11-01T07:00:00.000+01:002017-11-01T09:00:58.484+01:00The Wizard and the Magician<div class="separator" style="clear: both; text-align: center;"><a href="https://4.bp.blogspot.com/-84YXoIY0LJg/Wfl-_h1EaqI/AAAAAAAAD1w/3t8CwNboxG8GJhEo-mXl7VUMu3FsJicpwCLcBGAs/s1600/houdiniedison.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="665" data-original-width="828" height="514" src="https://4.bp.blogspot.com/-84YXoIY0LJg/Wfl-_h1EaqI/AAAAAAAAD1w/3t8CwNboxG8GJhEo-mXl7VUMu3FsJicpwCLcBGAs/s640/houdiniedison.jpg" width="640" /></a></div><div class="separator" style="clear: both; text-align: center;"><br /></div><br />&nbsp;We all know, at least at a surface level, the names Thomas Edison and Harry Houdini.&nbsp; One, a champion of the scientific method, and the other, a dazzling showman.<br /><br />But wait -- which one, exactly, is which?<br /><br />I'll begin with a short anecdote.<br /><br />In a letter,* Harry Houdini wrote about paying a visit to the acclaimed psychic Bert Reese.&nbsp; Reese would have his clients write their thoughts onto pieces of paper, fold them into presumably illegible "pellets", which he would then telepathically read.&nbsp; Houdini wrote a detailed explanation of Reese's method, concluding that this was clearly not telepathy, but the type of stage magic trick that he, Houdini, knew well how to execute.&nbsp; The letter's response came, indignant, saying Reese must be credible since even the great scientist Edison believed in his abilities.&nbsp; Houdini replied,<br /><br /><blockquote class="tr_bq"><span style="font-size: x-large;">"That he fooled Edison does not surprise me.&nbsp; He would have surprised me if he had <i>not</i> fooled Edison."</span></blockquote><br />Having delivered one of the sickest historical burns of all time, Houdini dropped his proverbial mic and went forward with renewed purpose.&nbsp; He was on a mission to defraud psychics and mediums.<br /><br /><br /><br />Thomas Edison, who never physically interacted with Houdini, was determined to scientifically support his belief in the paranormal.&nbsp; He conducted experiments on psychics, and was apparently convinced by his results -- which he conveniently never shared.&nbsp; As a celebrated innovator, he came to be known as <i>The Wizard of Menlo Park</i>, evidence of the extent to which Edison enjoyed wreathing his scientific invention in a kind of mysticism.&nbsp; "The phonograph will turn that ancient dream of immortality into reality," he wrote of his own invention.&nbsp; It's this kind of huckster phraseology that leads many** to suppose that his persistence on understanding the paranormal (and his <a href="http://www.radio-science.net/2017/10/edisons-necrophone.html" target="_blank">alleged work on the necrophone</a>) was a sort of hoax intended never to succeed, but rather to further embellish a lasting, supernatural self-image.&nbsp; <br /><br />Meanwhile, Houdini was picking off mediums, psychics, telepaths, and performers of séances like money-grubbing flies.&nbsp; He found them "morally repugnant", not the use of stage magic in itself, but that performers would use it as a way to exploit grieving clients desiring to communicate with lost loved ones.&nbsp; His skills at sleight-of-hand and escapology were his weapons to reveal the tricks with which psychics and mediums built their trade.<br /><br /><blockquote class="tr_bq"><span style="font-size: small;"><span style="font-size: large;">"The singularity of Houdini's approach to magic was that he wanted to free his public from the belief in supernatural powers.&nbsp; His escape philosophy was a way of performing a collective catharsis from the invisible powers of the State, physically represented by handcuffs." </span>(<a href="http://www.academia.edu/430370/Edison_Vs._Houdini" target="_blank">Source</a>)</span></blockquote><br />So we find, paradoxically, the roles of scientist and magician inverted: A scientist who took advantage of the ignorance of the masses to enable his own superhuman persona, and a magician who used logic to publicly expose those intending to beguile.<br /><br />I know who I vote for.<br /><br /><br /><div class="separator" style="clear: both; text-align: center;"><a href="https://1.bp.blogspot.com/-Ai0045nCWao/WeSrgAZjQII/AAAAAAAADzI/IqEOlNO4-ZsnEoXoGpAHS-1Zdwh2g0TxwCLcBGAs/s1600/harry-houdini.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="332" data-original-width="624" height="212" src="https://1.bp.blogspot.com/-Ai0045nCWao/WeSrgAZjQII/AAAAAAAADzI/IqEOlNO4-ZsnEoXoGpAHS-1Zdwh2g0TxwCLcBGAs/s400/harry-houdini.jpg" width="400" /></a></div><div style="text-align: center;"><span style="font-size: x-small;"><strike>Also, he's just such a babe</strike></span></div><br /><br /><br /><br /><br />~~~~~~~~~~~~~~~~~~<br /><br />* The letter correspondence in question was with Harry Houdini's close friend, none other than Arthur Conan Doyle -- the inventor of what is perhaps the universal symbol of logical reasoning and rationality, Sherlock Holmes.&nbsp; Keeping with the theme of this post, I'll mention here the irony that Doyle was also himself a devoted spiritualist, which aggravated his friendship with Houdini and later led to their falling out.<br /><br />** I among themAlessandra Serranohttp://www.blogger.com/profile/01802487750123767305noreply@blogger.com0tag:blogger.com,1999:blog-3384111523585932540.post-382613022002636542017-10-31T06:30:00.000+01:002017-10-31T06:30:04.495+01:00Edison's Necrophone<div class="separator" style="clear: both; text-align: center;"><a href="https://4.bp.blogspot.com/-3lvf4Pkg380/WdNL09j53SI/AAAAAAAADvc/nLIXiCiQUd8jseJlQSIw7ot6fV8SGc1xwCLcBGAs/s1600/xlg_edison_spirit_1%2Bcopy.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="502" data-original-width="626" height="512" src="https://4.bp.blogspot.com/-3lvf4Pkg380/WdNL09j53SI/AAAAAAAADvc/nLIXiCiQUd8jseJlQSIw7ot6fV8SGc1xwCLcBGAs/s640/xlg_edison_spirit_1%2Bcopy.jpg" width="640" /></a></div><br />It's difficult, in our world full of Skype and Snapchat and radio science, to imagine a time when the act of producing a wireless signal -- either a sound controlled at a distance or a voice disembodied from its owner -- was considered deeply unsettling.<br /><br />For context, when Marconi first wrote to the Ministry of Posts and Telegraphs in the 1890s to ask for funding to develop his wireless telegraph (or radio), the letter was dismissed with a comment that the idea was only worthy of an inmate at the local insane asylum.&nbsp; At a similar time, Thomas Edison's phonograph had its first public demonstration at the Academy of Sciences in Paris, where people heard ghostly voices, without faces, emerging from the engravings on cylinders inside a machine.&nbsp; One acclaimed academic grabbed the demonstrator by the lapel, claiming: It was all a trick! An acoustic illusion!<br /><br />"The phonograph," writes Edison, "will turn that ancient dream of immortality into reality." <br /><br />This era of invention also saw the rise of a new movement: Spiritualism.&nbsp; Massive amounts of people became fascinated with the idea of communication with the "Realms Beyond", including many scientists.&nbsp; Psychics, mediums, telepaths, and magicians were profiting immensely on these beliefs.&nbsp; William Crookes, inventor of the vacuum and cathode tube, attempted to use his new devices to create a machine that would project images of ghosts onto a screen, and made several attempts to photograph ghosts.*&nbsp; <br /><br />Meanwhile, Edison worked with morbid fascination on the topic of the threshold between life and death.**<br /><br /><br /><div class="separator" style="clear: both; text-align: center;"><a href="https://1.bp.blogspot.com/-9bNavfXm4QI/WdSLRDLRcsI/AAAAAAAADvs/4Xa9B3ve54kFdt6bNC-xuJHleNe6z3_oQCLcBGAs/s1600/necrophone_14%25C2%25A9Wainwright_Evans_FATE.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="527" data-original-width="355" height="640" src="https://1.bp.blogspot.com/-9bNavfXm4QI/WdSLRDLRcsI/AAAAAAAADvs/4Xa9B3ve54kFdt6bNC-xuJHleNe6z3_oQCLcBGAs/s640/necrophone_14%25C2%25A9Wainwright_Evans_FATE.jpg" width="428" /></a></div><br />In 1920, Edison announced in <i>Scientific American</i> his plans to work on a machine that would "provide the spiritualists with a device that would give them the opportunity to work strictly within the boundaries of science."&nbsp; He believed that there were "residues of memories, little voices" floating around in the air, that his device could capture and make audible.<br /><br /><blockquote class="tr_bq">"Like a microphone amplifies several times the volume and range of the human voice, my valve greatly amplifies any force of energy through with the spirit could show itself... By coincidence one of my assistants in this journey has just passed away.&nbsp; Since he exactly knew what I was after, I would guess he will be the first to use my device, provided of course he is able to do so!"</blockquote><br />It's difficult to know for certain Edison's level of sincerity.&nbsp; Was it a genuine pursuit of explanation for the paranormal?&nbsp; Or an attempt at creating an elaborate image?&nbsp; Or, that common hubris: the disregard of truth in pursuit of what he merely wanted to be true?<br /><br /><br /><br /><br />~~~~~~~~~~~<br /><br />* It is amusing to me that Crookes's cathode tubes were later used to project images of ghosts of their own -- in the form of television.<br /><br />** <a href="https://www.youtube.com/watch?v=aREqrfVJQwU" target="_blank"><i>Le Royaume de l'Au-delà</i></a>, or "The Realms Beyond"; a chapter title in Edison's autobiographical work.<br /><br />Alessandra Serranohttp://www.blogger.com/profile/01802487750123767305noreply@blogger.com0tag:blogger.com,1999:blog-3384111523585932540.post-20077193941948799032017-10-30T08:00:00.000+01:002017-10-30T08:00:00.648+01:00Sunrise at Jicamarca Radio Observatory<div dir="ltr" style="text-align: left;" trbidi="on">Here's a quaint photo from Jicamarca on one of the mornings. The sun had just come up over the mountains and as usual, everything was relatively foggy.<br /><table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody><tr><td style="text-align: center;"><a href="https://2.bp.blogspot.com/-D6sazOAqS58/WfXhvoa9i2I/AAAAAAAAPsM/Y3uFoUBmPooq72oRi1g0GhhWNDZgNR20wCLcBGAs/s1600/IMG_5941.JPG" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="1200" data-original-width="1600" height="240" src="https://2.bp.blogspot.com/-D6sazOAqS58/WfXhvoa9i2I/AAAAAAAAPsM/Y3uFoUBmPooq72oRi1g0GhhWNDZgNR20wCLcBGAs/s320/IMG_5941.JPG" width="320" /></a></td></tr><tr><td class="tr-caption" style="text-align: center;">The two Alpaccas that take care of mowing the lawn at Jicamarca are already up.</td></tr></tbody></table></div>Juha Vierinenhttps://plus.google.com/108603317449900180332noreply@blogger.com0tag:blogger.com,1999:blog-3384111523585932540.post-50123675086861359962017-10-29T15:11:00.003+01:002017-10-29T15:16:16.605+01:00Flowers blooming on the floodplain<div dir="ltr" style="text-align: left;" trbidi="on">This year Peru suffered from the worst flash flooding (Huayco) in years. The water is now gone, and things are now dry. This year I've seen a lot more plant life on the Huayco plain than I usually do. There are flowers everywhere. There are also some interesting insects too. I've been staying at the observatory for a week, participating in a campaign of observations that are trying to observe radar echoes from the Sun.<br /><table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody><tr><td style="text-align: center;"><a href="https://4.bp.blogspot.com/-_tObWDVHTT8/WfXgLXuE-_I/AAAAAAAAPrs/Xerh7LhRgc0y49EBofy1aA9UO7bbBMOCgCLcBGAs/s1600/IMG_5956.JPG" imageanchor="1" style="margin-left: auto; margin-right: auto; text-align: center;"><img border="0" data-original-height="1200" data-original-width="1600" height="240" src="https://4.bp.blogspot.com/-_tObWDVHTT8/WfXgLXuE-_I/AAAAAAAAPrs/Xerh7LhRgc0y49EBofy1aA9UO7bbBMOCgCLcBGAs/s320/IMG_5956.JPG" width="320" /></a></td></tr><tr><td class="tr-caption" style="text-align: center;">In the far distance, you can see the Jicamarca Radio Observatory. The whole valley was pretty much covered with water flowing during this years flash flooding. On the right is Sterling Hill, and on the left Merri Hill</td></tr></tbody></table><br /><br /><table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody><tr><td style="text-align: center;"><a href="https://3.bp.blogspot.com/-CYr4Ny_k7CA/WfXgHpLPQuI/AAAAAAAAPrk/YfybnuC2QFkm_dw_5Ezk17DfEscxuWhLwCLcBGAs/s1600/IMG_5951.JPG" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="1200" data-original-width="1600" height="240" src="https://3.bp.blogspot.com/-CYr4Ny_k7CA/WfXgHpLPQuI/AAAAAAAAPrk/YfybnuC2QFkm_dw_5Ezk17DfEscxuWhLwCLcBGAs/s320/IMG_5951.JPG" width="320" /></a></td></tr><tr><td class="tr-caption" style="text-align: center;">Plant life!</td></tr></tbody></table><br /><table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody><tr><td style="text-align: center;"><a href="https://4.bp.blogspot.com/-ZtuzIMtpj1c/WfXgIq3CNcI/AAAAAAAAPro/mgLSDV1FyRwTU6YHxA3iFXZPqXmHoOQ_QCLcBGAs/s1600/IMG_5955.JPG" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="1200" data-original-width="1600" height="240" src="https://4.bp.blogspot.com/-ZtuzIMtpj1c/WfXgIq3CNcI/AAAAAAAAPro/mgLSDV1FyRwTU6YHxA3iFXZPqXmHoOQ_QCLcBGAs/s320/IMG_5955.JPG" width="320" /></a></td></tr><tr><td class="tr-caption" style="text-align: center;">Flowers</td></tr></tbody></table><br /><table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody><tr><td style="text-align: center;"><a href="https://1.bp.blogspot.com/-oc4fd8KJot4/WfXgX4TaUaI/AAAAAAAAPrw/xvpChsK-BvE-bOOBWdxJiBCNZst2ZSIhgCLcBGAs/s1600/IMG_5963.JPG" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="1200" data-original-width="1600" height="240" src="https://1.bp.blogspot.com/-oc4fd8KJot4/WfXgX4TaUaI/AAAAAAAAPrw/xvpChsK-BvE-bOOBWdxJiBCNZst2ZSIhgCLcBGAs/s320/IMG_5963.JPG" width="320" /></a></td></tr><tr><td class="tr-caption" style="text-align: center;">More flowers</td></tr></tbody></table><br /><table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody><tr><td style="text-align: center;"><a href="https://4.bp.blogspot.com/-TA1Ch6BV_Sk/WfXgaNg05BI/AAAAAAAAPr0/IWVkHhfD7zAlOeZM-8lMoqe3CDXxx8NNACLcBGAs/s1600/IMG_5948.JPG" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="1200" data-original-width="1600" height="240" src="https://4.bp.blogspot.com/-TA1Ch6BV_Sk/WfXgaNg05BI/AAAAAAAAPr0/IWVkHhfD7zAlOeZM-8lMoqe3CDXxx8NNACLcBGAs/s320/IMG_5948.JPG" width="320" /></a></td></tr><tr><td class="tr-caption" style="text-align: center;">Even more flowers.</td></tr></tbody></table><br /><table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody><tr><td style="text-align: center;"><a href="https://3.bp.blogspot.com/-YijV9K69C4g/WfXgbYI0RZI/AAAAAAAAPr4/L95hR9SaXZsdzufvLk4QX6GgpHftYwfdgCLcBGAs/s1600/IMG_5947.JPG" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="1200" data-original-width="1600" height="240" src="https://3.bp.blogspot.com/-YijV9K69C4g/WfXgbYI0RZI/AAAAAAAAPr4/L95hR9SaXZsdzufvLk4QX6GgpHftYwfdgCLcBGAs/s320/IMG_5947.JPG" width="320" /></a></td></tr><tr><td class="tr-caption" style="text-align: center;">Again, I have no idea what species this is. It looks like a big sand colored locust.</td></tr></tbody></table><div class="separator" style="clear: both; text-align: center;"><br /></div><br /></div>Juha Vierinenhttps://plus.google.com/108603317449900180332noreply@blogger.com1tag:blogger.com,1999:blog-3384111523585932540.post-79065894413393990772017-10-28T08:00:00.000+02:002017-10-28T08:00:15.350+02:00Anglo-European translationThis is an old one. It has been going about the Interweb for years now. But it is so true.<br /><br />So, as a refresher course, allow me to post it again.<br /><br /><div class="separator" style="clear: both; text-align: center;"><a href="https://3.bp.blogspot.com/-MlKPrpIRFEg/We43q1nQqbI/AAAAAAAAEZo/kLLFITLp9xY3rI6xDkSQG-mRg1lpeDEtQCLcBGAs/s1600/angloeu_translation.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="1045" data-original-width="748" height="320" src="https://3.bp.blogspot.com/-MlKPrpIRFEg/We43q1nQqbI/AAAAAAAAEZo/kLLFITLp9xY3rI6xDkSQG-mRg1lpeDEtQCLcBGAs/s320/angloeu_translation.png" width="229" /></a></div><br /><br />PS:&nbsp; Note that here EU includes the EEA (Switzerland, Iceland, Åland... and <b>NORWAY</b>!)Derek McKayhttp://www.blogger.com/profile/05310213628364646890noreply@blogger.com0tag:blogger.com,1999:blog-3384111523585932540.post-24445785963287567102017-10-27T08:00:00.000+02:002017-10-27T08:00:08.566+02:00Ominous cloudsJust a photo today... grey leaden skies over <a href="http://kaira.uit.no/">KAIRA</a>, the Kilpisjärvi Atmospheric Imaging Receiver Array.<br /><br /><div class="separator" style="clear: both; text-align: center;"><a href="https://2.bp.blogspot.com/-02bJRHsm_wc/We446SYFqCI/AAAAAAAAEZs/1X0BgFTwLYIzLVFEcxXA2mqUW860qZ7yQCLcBGAs/s1600/Valokuva4180.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="1200" data-original-width="1600" height="240" src="https://2.bp.blogspot.com/-02bJRHsm_wc/We446SYFqCI/AAAAAAAAEZs/1X0BgFTwLYIzLVFEcxXA2mqUW860qZ7yQCLcBGAs/s320/Valokuva4180.jpg" width="320" /></a></div><br />Sure enough, within half an hour or so, the skies opened up. I had a long walk home... and was thoroughly soaked by the time I reached shelter. The antennas along the lower edge of the photograph are the KAIRA LBA (Low-Band Antenna) Array. The mountains are those in the region of Iso-Malla.Derek McKayhttp://www.blogger.com/profile/05310213628364646890noreply@blogger.com0tag:blogger.com,1999:blog-3384111523585932540.post-87436209369923018072017-10-26T06:30:00.000+02:002017-11-06T10:52:51.247+01:00Lunar Cave<br /><div class="separator" style="clear: both; text-align: center;"><a href="https://apod.nasa.gov/apod/image/1710/MariusHills_LO2LRO_1673.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="509" data-original-width="800" height="406" src="https://apod.nasa.gov/apod/image/1710/MariusHills_LO2LRO_1673.jpg" width="640" /></a></div><div style="text-align: center;">LRO radar image of "hole in the Moon" in the region of Marius Hills.&nbsp; (Image credit: <a href="https://www.nasa.gov/" target="_blank">NASA</a> and <a href="https://nssdc.gsfc.nasa.gov/nmc/spacecraftDisplay.do?id=1966-100A" target="_blank">Lunar Orbiter 2</a>.&nbsp; Inset: <a href="https://www.nasa.gov/mission_pages/LRO/overview/index.html" target="_blank">LRO</a>)</div><br />In 2009, Japan's SELENE spacecraft imaged a curious hole in the Lunar surface.&nbsp; Some follow-ups from the Lunar Reconnaissance Orbiter (LRO) were able to determine that the hole was some 100 meters deep and several hundred meters wide.<br /><br />Recently, <a href="http://onlinelibrary.wiley.com/doi/10.1002/2017GL074998/full" target="_blank">a re-analysis of radar data from SELENE</a> was able to show an unusual secondary echo pattern coming from the region.&nbsp; These findings indicate a series of underground lava tubes, formed during the Moon's active volcanic period billions of years ago, which extend downward for several kilometers and stretch out perhaps 100 kilometers.<br /><br />The buzz around this discovery is the possibility of using these caves to house potential Moon colonies -- or even future cities.<br /><br />Though, of course, these developments are far into the future, I can't pretend I'm not excited at the prospect of my own little Moon-Cave.<br /><br /><br /><br /><br />Alessandra Serranohttp://www.blogger.com/profile/01802487750123767305noreply@blogger.com0tag:blogger.com,1999:blog-3384111523585932540.post-27586618186572682862017-10-24T06:30:00.000+02:002017-10-24T06:30:15.160+02:00Cat Scans<div class="separator" style="clear: both; text-align: center;"><a href="https://2.bp.blogspot.com/-ab1HFY9xNLc/We2w_JZ5f6I/AAAAAAAADz4/QlFeVDtEqbYzgcHZw1LwAtOP3nLyhG6kQCLcBGAs/s1600/actual.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="291" data-original-width="269" src="https://2.bp.blogspot.com/-ab1HFY9xNLc/We2w_JZ5f6I/AAAAAAAADz4/QlFeVDtEqbYzgcHZw1LwAtOP3nLyhG6kQCLcBGAs/s1600/actual.png" /></a></div>For our inverse problems course, we are working on 2-D tomography.<br /><br />To the programming layman (which I consider myself mostly also to be), this is an attempt to simulate the same process occurring in a CT-scan or X-ray machine.&nbsp; You have an unknown object, surrounded by a user-defined number of transmitters and sensors.&nbsp; The transmitters shoot out some probe along one line (x-rays, for instance), the receiver collects whatever passes through the object in the center.&nbsp; If you do this enough times, you can combine your lines to estimate the object inside.<br /><br />And, of course, I couldn't resist a good cat pun.<br /><br />I wrote a code that gives a graphical representation of the transmitter/sensor setup, with red dots representing the transmitters, and blue dots representing receivers.&nbsp; Beside them are two different mathematical approximations of the object inside, using a Least Squares (LS) method and an A Priori (MAP) method.<br /><br /><br />&nbsp;First was a very sparse setup, with only 9 transmitters with 5 beams/sensors:<br /><div class="separator" style="clear: both; text-align: center;"><a href="https://4.bp.blogspot.com/--HFnMSGty1Q/We2-uuQ_sTI/AAAAAAAAD08/jXVuxU2uDgsnXRzF1IRszPlEBY7X53PMACLcBGAs/s1600/c9p5.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="296" data-original-width="926" height="204" src="https://4.bp.blogspot.com/--HFnMSGty1Q/We2-uuQ_sTI/AAAAAAAAD08/jXVuxU2uDgsnXRzF1IRszPlEBY7X53PMACLcBGAs/s640/c9p5.jpg" width="640" /></a></div><div style="text-align: center;">Clearly underestimated!&nbsp; Thought geometrically aesthetically pleasing. </div><br /><br />&nbsp;Next, let's inch our way up, with different scenarios to see the "interference" patterns, and how they affect our estimates.&nbsp; The following is with 10 transmitters, each with 50 receivers:<br /><div class="separator" style="clear: both; text-align: center;"><a href="https://1.bp.blogspot.com/-4QackCbwdmA/We2-uF47KrI/AAAAAAAAD0w/Xgcf1lyd-lE35P-50dZmM2UnP_Dg5THEwCLcBGAs/s1600/c10p50.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="292" data-original-width="935" height="198" src="https://1.bp.blogspot.com/-4QackCbwdmA/We2-uF47KrI/AAAAAAAAD0w/Xgcf1lyd-lE35P-50dZmM2UnP_Dg5THEwCLcBGAs/s640/c10p50.jpg" width="640" /></a></div><div style="text-align: center;">&nbsp;The LS estimate can't make heads nor tails of our kitty.&nbsp; The MAP estimate starts to approximate the original, though was dubbed by a colleague as "Cthulhu Cat."</div><br /><br />Now, how about a more even distribution of transmitters and receivers?&nbsp; 30 transmitters, each with 30 receivers: <br /><br /><div class="separator" style="clear: both; text-align: center;"><a href="https://3.bp.blogspot.com/-z-ZZpkSJjA0/We2-uKzzoDI/AAAAAAAAD00/JeJq4TOuRZMceoFlTXWaLHdUsBQEM70nACLcBGAs/s1600/c30p30.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="291" data-original-width="952" height="194" src="https://3.bp.blogspot.com/-z-ZZpkSJjA0/We2-uKzzoDI/AAAAAAAAD00/JeJq4TOuRZMceoFlTXWaLHdUsBQEM70nACLcBGAs/s640/c30p30.jpg" width="640" /></a></div><div style="text-align: center;">The LS estimate still struggles.&nbsp; There is a slight "ripple" pattern in the MAP estimate, but it's more or less homogeneously bad.</div><div style="text-align: center;"><br /></div><div style="text-align: center;"><br /></div><div style="text-align: left;">We tried many receivers for few transmitters, how about the other way around?&nbsp; The next image is with 50 transmitters, each with only 10 receivers:</div><br /><div class="separator" style="clear: both; text-align: center;"><a href="https://4.bp.blogspot.com/-Wwu1xYe5MUI/We2-uPLX1EI/AAAAAAAAD0s/N2IICa0DaYYF93v8DaUP0MCf7GKcJTNkACLcBGAs/s1600/c50p10.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="296" data-original-width="917" height="206" src="https://4.bp.blogspot.com/-Wwu1xYe5MUI/We2-uPLX1EI/AAAAAAAAD0s/N2IICa0DaYYF93v8DaUP0MCf7GKcJTNkACLcBGAs/s640/c50p10.jpg" width="640" /></a></div><div style="text-align: center;">LS is at least beginning to have postitive values, but still nothing concrete.&nbsp; In a setup like this, we can see a really strong "ripple" interference pattern in the MAP estimate.</div><br /><br />The above examples show that keeping the number of receivers and transmitters roughly equal is probably the best way to image your cat.&nbsp; So let's bump up the number, with 50 transmitters and 50 receivers: <br /><div class="separator" style="clear: both; text-align: center;"><a href="https://2.bp.blogspot.com/-OWTj9OKwZSw/We2-uTg0k5I/AAAAAAAAD04/VDBpL5U5y1QROBAO2GyniJsjZaif57teACLcBGAs/s1600/c50p50.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="289" data-original-width="909" height="202" src="https://2.bp.blogspot.com/-OWTj9OKwZSw/We2-uTg0k5I/AAAAAAAAD04/VDBpL5U5y1QROBAO2GyniJsjZaif57teACLcBGAs/s640/c50p50.jpg" width="640" /></a></div><div style="text-align: center;">LS is starting to dream about cats.&nbsp; For the MAP... success!!&nbsp; Though still a bit underestimated. </div><br /><br />At what point does the Least Squares estimate actually start to produce results?&nbsp; Let's keep going higher, now with 60 transmitters and 60 receivers: <br /><br /><div class="separator" style="clear: both; text-align: center;"><a href="https://2.bp.blogspot.com/-ZyyLfcyxRmM/We2-ujXzVUI/AAAAAAAAD1A/epCFhWcKRKML7vSpfCwygbP86GY_7Oy5ACLcBGAs/s1600/c60p60.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="284" data-original-width="912" height="198" src="https://2.bp.blogspot.com/-ZyyLfcyxRmM/We2-ujXzVUI/AAAAAAAAD1A/epCFhWcKRKML7vSpfCwygbP86GY_7Oy5ACLcBGAs/s640/c60p60.jpg" width="640" /></a></div><div class="separator" style="clear: both; text-align: center;">At last, a successful Cat Scan!&nbsp; Now, with enough information, we can see that the LS estimate produces a cleaner result than the MAP estimate.</div><br /><br /><br /><br /><br /><br /><br /><br /><br /><br />Alessandra Serranohttp://www.blogger.com/profile/01802487750123767305noreply@blogger.com1tag:blogger.com,1999:blog-3384111523585932540.post-65258324517933105492017-10-23T07:00:00.000+02:002017-10-23T10:42:23.719+02:00Rainbow Fog?<div class="separator" style="clear: both; text-align: center;"><a href="https://2.bp.blogspot.com/-BJuwab2geKY/Wey7I8Rl2oI/AAAAAAAADzo/D8EuYakQHYEJd5PoH0WW8quqM1HNCGHPACLcBGAs/s1600/IMG_1387.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="560" data-original-width="1600" height="224" src="https://2.bp.blogspot.com/-BJuwab2geKY/Wey7I8Rl2oI/AAAAAAAADzo/D8EuYakQHYEJd5PoH0WW8quqM1HNCGHPACLcBGAs/s640/IMG_1387.jpg" width="640" /></a></div><br /><br />Call out to all physicists...<br /><br />Why is the rainbow flat?&nbsp; I MUST KNOW. Alessandra Serranohttp://www.blogger.com/profile/01802487750123767305noreply@blogger.com2tag:blogger.com,1999:blog-3384111523585932540.post-37921204080935929352017-10-22T08:00:00.000+02:002017-10-22T12:25:41.114+02:00KAIRA jänis attackThere has been a jänis attack at KAIRA. <a href="http://kaira.uit.no/">KAIRA</a> is the Kilspisjärvi Atmospheric Imaging Receiver Array, which we support from here at Tromsø. A jänis is the Finnish name for what would be called a "Finnish Mountain Hare" in English. These creatures live in Lapland and a quite cute.<br /><br /><br /><table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody><tr><td style="text-align: center;"><a href="https://1.bp.blogspot.com/-9W0P8RlkXQY/Weu_pVwhSMI/AAAAAAAAEY0/ZqaXoWub5P0yGKs1AdpxtJd37qbwwky9gCLcBGAs/s1600/hba_janis.jpg" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="683" data-original-width="1023" height="213" src="https://1.bp.blogspot.com/-9W0P8RlkXQY/Weu_pVwhSMI/AAAAAAAAEY0/ZqaXoWub5P0yGKs1AdpxtJd37qbwwky9gCLcBGAs/s320/hba_janis.jpg" width="320" /></a></td></tr><tr><td class="tr-caption" style="text-align: center;">Mountain leveret under the High-Band Antenna array (Photo: J. Keskitalo)</td></tr></tbody></table><br /><br />But don't be fooled<br /><br />They are trained antenna killers!<br /><br />For some reason, like like to gnaw on cables. And the elastic guy lines of the KAIRA Low-Band Antenna (LBA) array aerials are a particular favourite. On the old KAIRA construction web log, I had often <a href="http://kaira.sgo.fi/search/label/janis">reported KAIRA jänis attacks</a>. Things have been quiet lately.<br /><br />However, in the last few days, we've noted the loss of signal from LBA antenna #L38. Puzzled, we've investigated to find out that at 18:42:40 UTC on 17-Oct-2017, there was a sudden loss of signal on receiver unit (RCU) #077 (which is the Y-polarisation of LBA #L38).<br /><br /><br /><div class="separator" style="clear: both; text-align: center;"><a href="https://3.bp.blogspot.com/-SQzMK5KtamU/WevAKLFAuJI/AAAAAAAAEY8/Q1_H5sGiTiI5FAO9kgwpjvZwD77_VOe8gCLcBGAs/s1600/out2.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="480" data-original-width="640" height="240" src="https://3.bp.blogspot.com/-SQzMK5KtamU/WevAKLFAuJI/AAAAAAAAEY8/Q1_H5sGiTiI5FAO9kgwpjvZwD77_VOe8gCLcBGAs/s320/out2.png" width="320" /></a></div><br /><br /><br />Some time later, there was a loss on RCU #076, which is the X-polarisation of the same antenna. This happened somewhat gradually over the course of approximately 1 hour, starting roughly at 07:50 UTC the next morning.<br /><br /><br /><br /><div class="separator" style="clear: both; text-align: center;"><a href="https://1.bp.blogspot.com/-VYIin7pBY1g/WevALcpUp4I/AAAAAAAAEZA/KQzGZw-ZCIY5s07sgcDB5ifpNPHfCOI1ACLcBGAs/s1600/out1.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="480" data-original-width="640" height="240" src="https://1.bp.blogspot.com/-VYIin7pBY1g/WevALcpUp4I/AAAAAAAAEZA/KQzGZw-ZCIY5s07sgcDB5ifpNPHfCOI1ACLcBGAs/s320/out1.png" width="320" /></a></div><br />The loss of the X-polarisation was somewhat gradual. It was accompanied by a deflection of the Y-polarisation too. Here are both traces, at around the time of the loss of the X-polarisation.<br /><br /><br /><div class="separator" style="clear: both; text-align: center;"></div><br /><br /><div class="separator" style="clear: both; text-align: center;"><a href="https://2.bp.blogspot.com/-obSnERIYZjI/WevAN6tN4NI/AAAAAAAAEZE/knV5Xhc9mX8kQ8coRvuuAB0h7sT4BhFpQCLcBGAs/s1600/out3.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="480" data-original-width="640" height="240" src="https://2.bp.blogspot.com/-obSnERIYZjI/WevAN6tN4NI/AAAAAAAAEZE/knV5Xhc9mX8kQ8coRvuuAB0h7sT4BhFpQCLcBGAs/s320/out3.png" width="320" /></a></div><br /><br /><div class="separator" style="clear: both; text-align: center;"><a href="https://1.bp.blogspot.com/-Vlv6yVQ2XkU/WevAPIoYGsI/AAAAAAAAEZI/wDDT8OilVQ486BjyZLpw8iXAV235RcnDACLcBGAs/s1600/out4.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="480" data-original-width="640" height="240" src="https://1.bp.blogspot.com/-Vlv6yVQ2XkU/WevAPIoYGsI/AAAAAAAAEZI/wDDT8OilVQ486BjyZLpw8iXAV235RcnDACLcBGAs/s320/out4.png" width="320" /></a></div><br /><br /><br /><br />Zooming in on the time range, it seems that the initial fall of the Y-polarisation happened quickly, within the space of a couple of seconds. Here is the sequence of the spectra as the fall occurred.<br /><br /><div class="separator" style="clear: both; text-align: center;"><a href="https://2.bp.blogspot.com/-mvpjD4cKnc0/WevAR7oADuI/AAAAAAAAEZM/p0Qw70fW76QH1XHR0cb2BKSCvMv8Tne2QCLcBGAs/s1600/out6.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="512" data-original-width="512" height="320" src="https://2.bp.blogspot.com/-mvpjD4cKnc0/WevAR7oADuI/AAAAAAAAEZM/p0Qw70fW76QH1XHR0cb2BKSCvMv8Tne2QCLcBGAs/s320/out6.png" width="320" /></a></div><br /><div style="text-align: center;"><a href="https://3.bp.blogspot.com/-VIN_GexWCvc/WevATJAO8WI/AAAAAAAAEZQ/MXFAHbbVnuoi1S-RgumJrrZCXbdM7gU9QCLcBGAs/s1600/out7.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="512" data-original-width="512" height="320" src="https://3.bp.blogspot.com/-VIN_GexWCvc/WevATJAO8WI/AAAAAAAAEZQ/MXFAHbbVnuoi1S-RgumJrrZCXbdM7gU9QCLcBGAs/s320/out7.png" width="320" /></a></div><br /><div style="text-align: center;"><a href="https://3.bp.blogspot.com/-rw-CSnvCQAs/WevAUjbuuUI/AAAAAAAAEZU/JHSP-56C4eIeXOmE6c9NE1UyfEdTiolcgCLcBGAs/s1600/out8.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="512" data-original-width="512" height="320" src="https://3.bp.blogspot.com/-rw-CSnvCQAs/WevAUjbuuUI/AAAAAAAAEZU/JHSP-56C4eIeXOmE6c9NE1UyfEdTiolcgCLcBGAs/s320/out8.png" width="320" /></a> </div><br /><br /><br />It is difficult to say exactly what happened, but my hypothesis is that the jänis chewed the elastic through at 18:42:40 UTC on 17-Oct-2017, causing the Y-polarisation to "short-out". The post remained upright and the X-polarisation continued operating. Then the next morning, the antenna slowly listed over and fell, possibly under the weight of the snow. Further snow has then covered it, rendering the antenna completely inoperative.<br /><br />Well, this will need to be fixed.<br /><br />The location is as follows (click to enlarge the plot, but the recent loss is the grey square near the bottom of the LBA array - otherwise marked in green on the status map, as we are currently observing in RCU mode 3).<br /><br /><br /><br /><div class="separator" style="clear: both; text-align: center;"><a href="https://4.bp.blogspot.com/-WiAEzbvzBtg/WevAcPDQuWI/AAAAAAAAEZY/ltKnP0oTMWIu1uXBO9CD3opV7gWKA_iIQCLcBGAs/s1600/kaira_status.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="500" data-original-width="500" height="320" src="https://4.bp.blogspot.com/-WiAEzbvzBtg/WevAcPDQuWI/AAAAAAAAEZY/ltKnP0oTMWIu1uXBO9CD3opV7gWKA_iIQCLcBGAs/s320/kaira_status.png" width="320" /></a></div><br /><br />Meanwhile, KAIRA continues operation with 47 antennas.<br /><br />Derek McKayhttp://www.blogger.com/profile/05310213628364646890noreply@blogger.com0